IMHO, I would recommend that you use your Ritek media for data file backup, then for burning movies, video, etc, I highly recommend the Verbatim 16X DVD+R media w/the media code MCC 004---that and the Taiyo Yuden 8X DVD+R media code#YUDEN000T02 (generally available online) are some of the best discs to use in that drive.
here is a link from videohelp.com w/the report on the media and where it was purchased. http://www.videohelp.com/dvdmedia.php?selectmedia=2487#comments
Burn the MCC 004 at 12X instead of 16x w/the Benq 1640--since it doesn't do full 16x as well as the Liteon 165P6S, and as for firmware on the unit, I think that BSLB would not be a bad choice.
feel free to do a quality test w/CD/DVD speed to verify, but that is the most readily available quality media here in the US. I buy most of mine at BestBuy on sale.
Finally, there are two types of MCC 004 you can buy--identified by the cake box descriptors--but I would be hard pressed to tell you which one is better--look at cdfreaks.com for more info. also, there is a post on cdfreaks that have the disc qualilty tests for single-layer discs on the 1640, generally referencing a specific firmware.
oh, one more thing, burn w/the free program ImgBurn versus nero, there is better support there and it was written by the author of DVDShrink.